A high-pressure discharge lamp is of a configuration in which a pair of electrodes are arranged opposite each other in an arc tube composed of quartz glass, a substance such as mercury being enclosed inside the arc tube. The lamp is lighted by supplying an alternating current to the pair of electrodes, and while lighted, an arc is maintained by a protrusion that is formed at the tip portion of each electrode. Further, the shape of the protrusion formed on the tip of each electrode main is maintained by carrying out an appropriate halogen cycle that accords with the high-voltage discharge lamp.
Typically, a discharge lamp lighting device is constructed to light a high-pressure discharge lamp by constant-power control (see Patent Document 1). This discharge lamp lighting device includes a DC/DC converter, a DC/AC inverter, a high-voltage generation unit, a current detection unit, a voltage detection unit, and a control unit.
The DC/DC converter converts the input direct-current voltage to direct-current voltage of a designated voltage value. The DC/AC inverter receives the direct-current voltage that is supplied from the DC/DC converter and generates an alternating-current square-wave current. The alternating-current square-wave current that is supplied from this DC/AC inverter is supplied to the discharge lamp by way of the high-voltage generation unit. The high-voltage generation unit generates a trigger voltage for use as the required dielectric breakdown at the time of starting ignition.
The voltage detection unit detects the voltage that is equivalent to the lamp voltage that is applied to the discharge lamp. The current detection unit detects the current that is equivalent to the lamp current that flows in the discharge lamp. The control unit calculates the lamp power on the basis of the lamp voltage that was detected in the voltage detection unit and the lamp current that was detected in the current detection unit and adjusts the output voltage of the DC/DC converter such that the lamp power becomes a predetermined power (for example, the rated power).
The above-described discharge lamp lighting device is provided in devices such as projectors, and many such products have already been introduced on the market.